WPF treeview sub nodes disappeared

Question

I'm new to wpf and xaml. I just built 4 complex tree views on separate tabs with the same type, data of which were loaded from a json file which is fixed. But I found something weird:

1. When the first time they are loaded, some nodes do not show the little triangle, which means it contains no sub items, but in fact they do. (I have a number on the parent node and it says "10").
2. This happens only on those nodes that are not in the viewable area of the tree. Which means if I scroll to the node, and then reload the tree, everything is ok. But if I scroll to a node which was not viewable when tree was loaded, there is a big chance that it does not show the triangle and sub items.
3. When I switch among those tabs, sometimes a tree changes as described above, even no scrolling happens.
4. Initialing the nodes with IsExpand = True / False does not make difference.

Here is the xaml:

<resultTrees:ResultTreeView x:Class="ChiSharedFormsWpf.ResultTrees.ChiTreeView"
                        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
                        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
                        xmlns:fa5="http://schemas.fontawesome.com/icons/"
                        xmlns:bsiIndexes="clr-namespace:ChiLibApiJson.BsiIndexes;assembly=ChiLibApiJson"
                        xmlns:dirTrees="clr-namespace:WpfUtilities.DirTrees;assembly=WpfUtilities"
                        xmlns:resultTrees="clr-namespace:ChiSharedFormsWpf.ResultTrees"
                        mc:Ignorable="d" FontFamily="Consolas"
                        MouseDoubleClick="ChiTreeView_OnMouseDoubleClick"
                        d:DesignHeight="450" Width="auto">
<Grid>
    <DockPanel HorizontalAlignment="Stretch">
        <TreeView Name="Tree" HorizontalAlignment="Stretch"
                  VirtualizingStackPanel.IsVirtualizing="True"
                  VirtualizingStackPanel.VirtualizationMode="Recycling"
                  ScrollViewer.HorizontalScrollBarVisibility="Disabled">
            <TreeView.Resources>
                <!-- Style the inactive selection the same as active -->
                <SolidColorBrush Color="LightBlue" x:Key="{x:Static SystemColors.HighlightBrushKey}" />
                <SolidColorBrush x:Key="{x:Static SystemColors.InactiveSelectionHighlightBrushKey}"
                                 Color="LightBlue" />
                <SolidColorBrush x:Key="{x:Static SystemColors.InactiveSelectionHighlightTextBrushKey}"
                                 Color="OrangeRed" />

                <HierarchicalDataTemplate DataType="{x:Type dirTrees:BriefTree}"
                                          ItemsSource="{Binding Items}">
                    <StackPanel>
                        <StackPanel Orientation="Horizontal">
                            <fa5:FontAwesome Icon="{Binding Icon}" Margin="0,2,5,0" />
                            <TextBlock Text="{Binding Root.Text}" FontFamily="微软雅黑, Consolas" />
                        </StackPanel>
                    </StackPanel>
                </HierarchicalDataTemplate>
                <HierarchicalDataTemplate DataType="{x:Type resultTrees:FileResultList}"
                                          ItemsSource="{Binding FileResultBriefs}">
                    <StackPanel Orientation="Horizontal"
                                MouseRightButtonUp="TreeNode_OnMouseRightButtonUp">
                        <fa5:FontAwesome Icon="{Binding Icon}" Margin="0,2,5,0" />
                        <TextBlock FontWeight="Bold" Text="{Binding Root.Text}" />
                        <TextBlock FontWeight="Bold" Text="{Binding FileResultBriefs.Count}" />
                    </StackPanel>
                </HierarchicalDataTemplate>
                <HierarchicalDataTemplate DataType="{x:Type dirTrees:DirAndFileResultTree}"
                                          ItemsSource="{Binding SubDirsAndFilesAndBadSmells}">
                    <StackPanel Orientation="Horizontal" Background="{Binding DirColorHex}"
                                MouseRightButtonUp="TreeNode_OnMouseRightButtonUp"
                                Tag="{Binding Root.DirName }">
                        <fa5:FontAwesome Icon="Regular_FolderOpen" Margin="0,2,5,0" />
                        <TextBlock FontWeight="Bold" Text="{Binding Index.Brief}" />
                        <TextBlock FontWeight="Bold" Text="{Binding Root.DirName}" />
                    </StackPanel>
                </HierarchicalDataTemplate>
                <HierarchicalDataTemplate DataType="{x:Type dirTrees:FileResultBrief}"
                                          ItemsSource="{Binding BadSmells}">
                    <StackPanel Orientation="Horizontal" Background="{Binding  Index.SoftColorHex}"
                                MouseLeftButtonDown="FileResult_OnMouseLeftButtonDown"
                                MouseRightButtonUp="TreeNode_OnMouseRightButtonUp"
                                Tag="{Binding  FileName}">
                        <fa5:FontAwesome Icon="Regular_FileCode" Margin="0,2,5,0" />
                        <TextBlock Text="{Binding Brief}" />
                        <TextBlock Text="{Binding FileName}" Margin="10 0"/>
                    </StackPanel>
                </HierarchicalDataTemplate>
                <HierarchicalDataTemplate DataType="{x:Type bsiIndexes:BadSmell}" ItemsSource="{Binding }">
                    <HierarchicalDataTemplate.ItemContainerStyle>
                        <Style TargetType="TreeViewItem">
                            <Style.Triggers>
                                <DataTrigger
                                    Binding="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=IsWarning }"
                                    Value="True">
                                    <Setter Property="Visibility" Value="Hidden" />
                                </DataTrigger>
                            </Style.Triggers>
                        </Style>
                    </HierarchicalDataTemplate.ItemContainerStyle>
                    <StackPanel Orientation="Horizontal"
                                MouseLeftButtonDown="BadSmell_OnMouseLeftButtonDown"
                                Tag="{Binding}">
                        <fa5:FontAwesome Icon="{Binding XamlIcon}"
                                         Foreground="{Binding Path=ForeColorHex}" Margin="0,2,5,0" />
                        <StackPanel>
                            <TextBlock Text="{Binding Path=LevelAndRuleNameAndExplanation}"
                                       FontFamily="微软雅黑, Consolas"
                                       Foreground="{Binding Path=ForeColorHex}" />
                            <TextBlock Text="{Binding Path=PositionAndDescription}"
                                       FontFamily="微软雅黑, Consolas"
                                       Foreground="{Binding Path=ForeColorHex}" />
                        </StackPanel>
                    </StackPanel>
                </HierarchicalDataTemplate>
                <DataTemplate DataType="{x:Type dirTrees:BriefString}">
                    <TextBlock Text="{Binding Path=Text}" Foreground="{Binding Path=ForeColorHex}"
                               FontFamily="微软雅黑, Consolas" />
                </DataTemplate>
                <DataTemplate DataType="{x:Type dirTrees:IgnoredDirString}">
                    <StackPanel MouseRightButtonUp="TreeNode_OnMouseRightButtonUp"
                                Tag="{Binding Text}" Orientation="Horizontal">
                        <fa5:FontAwesome Icon="Solid_Folder" Foreground="gray"></fa5:FontAwesome>
                        <TextBlock Text="{Binding Path=Text}"  Foreground="gray"
                                   TextDecorations="Strikethrough" 
                                   FontFamily="微软雅黑, Consolas" />
                    </StackPanel>
                </DataTemplate>
                <DataTemplate DataType="{x:Type dirTrees:IgnoredFileString}">
                    <StackPanel MouseRightButtonUp="TreeNode_OnMouseRightButtonUp"
                                Tag="{Binding Text}" Orientation="Horizontal">
                        <fa5:FontAwesome Icon="Regular_File" Foreground="gray"></fa5:FontAwesome>
                        <TextBlock Text="{Binding Path=Text}"  Foreground="gray"
                                   TextDecorations="Strikethrough" 
                                   FontFamily="微软雅黑, Consolas" />
                    </StackPanel>
                </DataTemplate>
            </TreeView.Resources>
            <TreeView.ItemContainerStyle>
                <Style TargetType="{x:Type TreeViewItem}">
                    <!-- <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=OneTime}" /> -->
                    <!-- <Setter Property="IsExpanded" Value="True" /> -->
                    <Setter Property="IsExpanded" Value="False" />
                </Style>
            </TreeView.ItemContainerStyle>
        </TreeView>
    </DockPanel>
</Grid>
</resultTrees:ResultTreeView>

Here is partial of the model:

public List<FileResultBrief> FileResultBriefs { get; set; } = new();
public List<DirAndFileResultTree> SubTrees { get; set; } = new();

[JsonIgnore]
public IList SubDirsAndFilesAndBadSmells => new CompositeCollection
{
    new CollectionContainer {Collection = IgnoredFiles.OrderBy(i => i.Text).ToList()},
    new CollectionContainer {Collection = FileResultBriefs},
    new CollectionContainer {Collection = IgnoredDirs.OrderBy(i => i.Text).ToList()},
    new CollectionContainer {Collection = SubTrees},
};

So far I highly adoubt that there might be some shared-reference error in the model. But I someone can figure out problems in the xaml would be really helpful. Because I know little of it's mechanism.

Thanks a lot.

Answer 1

Finally, removing

VirtualizingStackPanel.VirtualizationMode="Recycling"

or using

VirtualizingStackPanel.VirtualizationMode="Standard"

instead solves the problem. I added this line 2 weeks ago to improve the performance. According to https://docs.microsoft.com/en-us/dotnet/api/system.windows.controls.virtualizationmode?view=windowsdesktop-6.0, seems that if a treeview contains different kind of containers (which I think is almost always true) should not use recycling mode.

So it's design for list only?

And I adapted o_w's suggestion and change the list to ObservableList. It makes no difference in this case but might help later, thanks.